The present invention relates to a mobile telecommunication system and is particularly concerned with the handover of calls between two types of communication systems, particularly handover between a GSM and a UMTS network.
It has been generally proposed that it would be desirable to provide handover between a GSM and a UMTS network. However, this is not a straightforward task to accomplish and there are a number of problems to implement before this can be successfully achieved; the present invention is concerned with these problems. It is, however, more generally applicable to interoperability between networks using different protocols; in such a case, the terms used herein are to be construed as applying to the relevant equivalent components of the networks to which the invention is applied. Although aspects of the invention provide independent solutions to various aspects of the problems concerned with GSM and UMTS handover, all are concerned with this common problem and in particular are concerned with a novel solution in which an RNC of the UMTS network controls handover to a large extent.